Ordering Mechanism in Mysql - php

Question

I have a matter in PHP & Mysql Project.
Simply, I have two tables project and project features,
Every project has as specific features.
CREATE TABLE projects (
ID INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name varchar(255) NOT NULL
);
CREATE TABLE projects_features (
projectId INT NOT NULL,
name varchar(255) NOT NULL,
value varchar(255) NOT NULL,
weight INT NOT NULL
);
INSERT INTO projects VALUES (NULL,'project1');
INSERT INTO projects VALUES (NULL,'project2');
INSERT INTO projects_features VALUES (1,'Feature1','Feature1 Value',1);
INSERT INTO projects_features VALUES (2,'Feature2','Feature2 Value',2);
INSERT INTO projects_features VALUES (1,'Feature3','Feature3 Value',3);
INSERT INTO projects_features VALUES (2,'Feature4','Feature4 Value',4);
INSERT INTO projects_features VALUES (1,'Feature5','Feature5 Value',5);
I Get the Project features by:
SELECT * FROM projects_features WHERE projectId = 1 ORDER BY weight ASC;
So the bigger weight will be down and lower weight will be Up.
Now,
In My View I have move up and move down buttons, so I can re-sort project features.
I can firstly select the current item weight then select the upper item weight ,
then type two update queries to exchange the weight between the two rows,
but it's not a professional way , I don't like to use four queries.
I need to do it in one query Instead of four queries.
Can anybody help please ?

Answer 1

Here's how I'd tackle this, assuming I've understood the question.
First, I'd add a featureId column to projects_features, and make (projectId, featureId) the composite primary key. This isn't actually necessary to my solution; it just makes the rest a whole lot easier. For the next part you need to be able to reference individual records in projects_features.
Next, I'd have the Move buttons populate an array in PHP, like
$update_list = array();
$update_list[i] = array(':project_id' => $proj_id,
':feature_id' => $feat_id,
':new_weight' => $weight);
Finally, I'd do the update through a PHP function that encapsulates the UPDATE statements, like this:
function updateWeights($update_array, $dbh)
{
$sql = 'UPDATE project_features
SET weight = :new_weight
WHERE projectId = :project_id
AND featureId = :feature_id'
$stmt = $dbh->prepare($sql);
foreach ($update_array as $update_item)
{
$stmt->execute($update_item);
}
}
Note I'm using PDO here; it could also be done with mysqli, although mysqli doesn't support named bind parameters so the syntax would be slightly different, something like
function updateWeights($update_array, $dbh)
{
$sql = 'UPDATE project_features
SET weight = ?
WHERE projectId = ?
AND featureId = ?'
$stmt = $dbh->prepare($sql);
foreach ($update_array as $update_item)
{
$stmt->bind_param('i', $update_item[':new_weight']);
$stmt->bind_param('i', $update_item[':project_id']);
$stmt->bind_param('i', $update_item[':feature_id']);
$stmt->execute();
}
}
Also note that I haven't actually run this code, and so make no representation that it is free of syntax or other errors.
I hope that helps.